1. Field of the Invention
The present invention relates to a solid state imaging device which includes a large number of photoelectric conversion elements arranged on a semiconductor substrate regularly in the row and column directions of the semiconductor substrate according to a previously set arrangement pattern respectively for detecting color components such as R (red), G (green) and B (blue).
2. Description of the Related Art
In a solid state imaging device which is employed in an apparatus such as a digital camera, in order to detect the image of a subject by every pixel of a two-dimensional image, a large necessary number of photoelectric conversion elements (generally, photodiodes) are two-dimensionally arranged in a tetragonal lattice manner. Also, in order to photograph a color image, generally, two or more photoelectric conversion elements respectively correlated with the respective colors, that is, R, G and B are regularly arranged in a two-dimensional manner in row and column directions according to a specific arrangement pattern.
Actually, to optimize the quality of a color image obtained by photographing, generally, two or more photoelectric conversion elements respectively correlated with the respective colors, that is, R, G and B are arranged according to a specific arrangement pattern called the Bayer arrangement pattern. Also, the characteristics of the colors to be detected by the respective photoelectric conversion elements are generally determined using color filters which are arranged on the front surfaces of the light receiving surfaces of the photoelectric conversion elements. That is, an optical filter transmitting only the R, an optical filter transmitting only the G and an optical filter transmitting only the B are arranged on the front surfaces of the light receiving surfaces of the respective photoelectric conversion elements according to the Bayer arrangement. When the optical filters are used, elements having the same characteristics can be used as the photoelectric conversion elements of the respective colors.
In the related art, for example, as disclosed in the JP-A-2004-055786, photoelectric conversion elements each having low detect sensitivity arranged in a tetragonal lattice manner and photoelectric conversion elements each having high detect sensitivity arranged in a tetragonal lattice manner are respectively arranged on a silicone substrate at mutually adjoining and shifted positions, thereby forming a honeycomb-shaped arrangement pattern.
The term “detect sensitivity of a photoelectric conversion element” means the characteristic of the photoelectric conversion element as to the quantity of signals that can be taken out from the photoelectric conversion element when a given quantity of light enters the photoelectric conversion element. In other words, a photoelectric conversion element having relatively high detect sensitivity can be defined such that, when the same quantity of light enters, it has a characteristic to be able to provide a larger quantity of signals than a photoelectric conversion element having relatively low detect sensitivity. Since the photoelectric conversion element having high sensitivity is able to provide a large quantity of signals with a small quantity of light, it is best suitable for photographing a subject of low luminance; however, when a large quantity of light enters, signals are saturated soon and, therefore, it is not suitable to photograph a subject of high luminance. Also, since the photoelectric conversion element having low detect sensitivity is not able to provide a large number of signals even when a large quantity of light enters, it is best suitable for photographing a subject of high luminance; however, when a small quantity of light enters, the quantity of signals to be provided by the element are too small and, therefore, it is not suitable to photograph a subject of low luminance.
In the above-structured solid state-imaging device, since, for every pixel to be detected, the photoelectric conversion element having low sensitivity and photoelectric conversion element having high sensitivity can be used at the same time, the light having a large quantity of light is detected by the photoelectric conversion element having low sensitivity and the light having a small quantity of light is detected by the photoelectric conversion element having high sensitivity, whereby the dynamic range of the image pickup characteristic of the solid state imaging device can be widened.
JP-A-11-355790 discloses arranging, on a silicon substrate, a first photosensitive element group formed by photosensitive elements for detecting a luminance component, arranged in a tetragonal lattice manner, and a second photosensitive element group formed by photosensitive elements for detecting a luminance component and photosensitive elements of two kinds for detecting respectively different color hue components, arranged in a tetragonal lattice manner, in shifted positions adjacent with each other, thereby forming a honeycomb-shaped arrangement pattern.
In a general solid state imaging device, there is employed a structure in which, in order to enhance the detect sensitivity of the respective photoelectric conversion elements, the light receiving areas of the respective photoelectric elements are set large, a micro lens is disposed on the front surface of the light receiving surface of each of the photoelectric conversion elements, whereby a larger quantity of light is allowed to enter the photoelectric conversion elements. However, when the number of photoelectric conversion elements is increased in order to enhance the resolution of the image to be photographed, the light receiving area of each photoelectric conversion element must be reduced, which makes it difficult to enhance the detect sensitivity of each photoelectric conversion element.
Especially, in the case of a solid state imaging device to photograph a color image, in order to detect the lights of the respective color components divided to R, G, B and the like, it is necessary to provide light dividing optical filters on the front surfaces of the receiving surfaces of the respective photoelectric conversion elements. However, because the transmittance of such optical filters is relatively low, the intensity of the light, which passes through the optical filters and is actually received by the photoelectric conversion elements, is attenuated, so that the sensitivity of the photoelectric conversion elements is lowered.
Suppose the sensitivity of the respective photoelectric conversion elements is low, for example, when a subject is photographed in a dark environment, a clear image cannot be obtained. Also, as disclosed in the JP-A-2004-055786, when, in a solid state imaging device, a photoelectric conversion element having low sensitivity and a photoelectric conversion element having high sensitivity are arranged at mutually adjoining positions, a signal of the photoelectric conversion element having low sensitivity and a signal of the photoelectric conversion element having high-sensitivity are combined together to thereby be able to broaden the dynamic range of the image pickup characteristic with respect to the brightness of the image; however, since the photoelectric conversion element having high sensitivity is easy to be influenced by the attenuation of the light due to the optical filter, the broadening effect of the dynamic range is reduced slightly.
Also in the combination of the detection wavelengths of the photosensitive elements employed for the first photosensitive element group and the second photosensitive element group as described in JP-A-11-355790, it is difficult to attain the color reproducibility and the improvement in sensitivity at the same time.